The Portrait of a Lady is one of the most important works of Henry James, especially stands out for the complexity of its heroine, Isabel Archer. In the novel, Isabel has made two life-changing decisions which seem to be in conflict with each other. The first is her refusal of Caspar Goodwood and Lord Warburton and choice of Gilbert Osmond. The second is Isabel’s return to her loveless marriage. Isabel’s choices are mostly owing to her personality. But in deeper sense, they are more closely linked with the author’s personal experiences and the historical background. In consequence, the thesis will focus on analyzing the driving forces behind Isabel’s choices. The thesis is divided into four parts, with the first part introducing Henry James and his creation of The Portrait of a Lady. By exploring these, the thesis would specify the aspects we need to study in analyzing the theme. Part two will elaborate on Isabel’s first decision, demonstrating that the historical background is playing a major role, largely influencing, or even deciding Isabel’s personality, which is mirrored in her choice of suitors and marriage. The third part, the thesis will discuss Isabel’s second decision, which is bewildering and controversial to many people. However, when we consider all the factors contributing to her choice, the ending of the novel is not that difficult to understand. In the second decision, the change of Isabel’s personality plays a larger part in the whole process. However, the historical background and the author’s personal thoughts still exist, which unwittingly limits the change and development to some extent. The conclusion part, in addition to summarizing all the already mentioned points, the paper will discuss the properties of the two choices, giving a personal opinion on whether it is a tragedy or not, and making bold assumptions about the real creation intention of the author.